A vertical processing furnace for processing substrates, e.g., semiconductor wafers may include a heating means, placed around a bell jar-shaped process tube and a substantially cylindrical liner that is coaxially disposed within the process tube. The upper end of the process tube may be closed, for example by a dome-shaped structure, whereas the lower end surface of the process tube may be open.
The liner may be open at its upper end and lower end. The lower end may be partially closed by a flange. An inner space bounded by the liner and the flange forms a process chamber in which wafers to be treated may be processed. Between the liner and the process tube is a circumferential space. The flange may be provided with an inlet opening for inserting a wafer boat carrying wafers into the inner space. The wafer boat may be placed on a door that is vertically moveably arranged and that is configured to close off the inlet opening in the flange.
The flange may further include at least one gas inlet that is in fluidum connection with the inner space bounded by the liner. Additionally, a gas exhaust may be provided that is in fluidum connection with the circumferential space between the liner and the process tube. This gas exhaust may be connected to a vacuum pump for pumping off gas from the circumferential space. This configuration may lead to a gas flow from the gas inlet at the lower end of the liner through the inner space of the liner upwards through the open end of the liner into the circumferential space and to the gas exhaust. The gas in the flow may be a reaction (process) gas for a deposition reaction on the wafers. This reaction gas may also deposit on other surfaces than the wafers within the vertical furnace.
A problem of vertical processing furnaces for processing substrates may be contamination in the inner space of the process tube.